Abstract

Abstract

Corn (Zea mays L.) yields in Minnesota have increased from the 2,010 kg/ha yield level of the pre-1930's to the current 6,290 kg/ha average. This increased yield can he attributed to a series of technological, cultural, and management practices adopted by farmers. My objective is to atlempt an analysis of the magnitude of the changes and the relative contributions to grain yield each practice has made over the 50-year time period. Only simple linear responses were estimated. No attempt has been made to evaluate the nature nor the magnitude of the interactions among the various management practices.

The change from open-pollinated to hybrid corn combined with the estimated 36.5 kg/ha/year genetic gain has produced 58% of the yield increase. Although each kilogram of applied commercial N has been estimated to increase yields by 18.9 kg of grain per kg for 47% of the gain in yield, the effects of less manure, and reduced N from mineralized organic matter actually produces a net N effect of 19%. Improved weed control by the use of herbicides on 93% of the hectarage has increased yields 23%.

Plant densities have increased by 19,130 plantdha contributing 47.4 kg/ha/1,000 plants for a total of 21% of the gain. Better soil drainage, fall plowing, and herbicides have permitted planting 10 days earlier for an average gain of 36.4 kg/ha/day and a total of 8% of the net increase. Drilling corn rather than hill dropping has contributed 8% and fall plowing has contributed 5% to current yields. Row spacing has decreased from 107 to 90 cm for a gain of 10.2 kglhaicm or 4% of the gain.

Rotation changes have had no net effect on N balance with increases in soybean [Glycine max (L.) Merr.] offsetting decreases in forage legume hectarage. However, there has been a negative effect of more hectares of corn following corn resulting in 3% loss from corn rootworm (Diabrotica spp.) and 7% loss due to the interference effect of corn following corn. Corn borer (Ostrinia nubilalis Hubner) became a problem in the 1940's and has reduced yield potential an average of 5%. Soil erosion has reduced yield potentials 8% over the 50 years. Other negative and unaccounted factors reduce the potential yields by 23%.

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